1. Field of the Invention
This invention relates to protective housings for cable connector plugs and the like and, more particularly, to a molded plastic hood therefor of simplified, rugged and inexpensive construction, and to a hood-connector plug assembly adapted for use with cables of varying diameter.
2. Description of the Prior Art
In the communications industry, in particular, multi-conductor, jacketed cable is extensively used, such as in telephone office switching equipment, PBX's and computers. To effect electrical connections between the terminating ends of such multi-conductor cables (typically of the 25 or 50 twisted wire pair type) to associated electrical equipment, connector plugs having an array of terminals of either the soldered or solderless type are employed.
In order to provide protection for the connections formed between the bare ends of the conductors and the respectively associated terminals of the connector plug, a protective hood is secured to the frame of the connector plug such that the completed connections are shielded from the outside. The hood is also formed to allow the outer jacket of the cable to be firmly secured thereto so that no adverse tensile forces can be imparted to any of the terminal-secured conductor ends confined within the housing during subsequent handling or use.
Such protective hoods have often been formed out of metal heretofore, with suitable fastening members, such as screws, being employed to secure the hood to the connector plug at either or both common ends thereof. In one embodiment of such a hood, eyelets formed in the hood adjacent the rearward end thereof, and ears formed in the rearward end of the connector plug, cooperate to effect securement. Such hoods have also typically included a rearward hood extension that is positioned to overly a section of the cable jacket, and been formed with downwardly extending and spaced clamping lugs adapted to straddle the jacket. The cable is secured to the hood by another metal screw which is inserted through apertures in these lugs adjacent their lower ends and tightened to clamp the lugs about the cable jacket. Since the position of the lugs and the locations of the screw apertures therein are fixed, it has been necessary heretofore to provide multiple or different sized inserts for use between the cable jacket and the clamping screw in order to accommodate cables of different diameter. As a result of their construction, metal protective hoods are not only more expensive than molded plastic hoods, but they have also required a number of loose parts that must be assembled. Moreover, a metal hood obviously cannot function as an insulative member to prevent the shorting out of any bare conductor ends that for some reason might become dislodged from the associated terminal of the connector plug after the assembly thereof.
A molded plastic hood intended to overcome some of the disadvantages of a metal hood assembly is disclosed in Scott J. Lapraik U.S. Pat. No. 3,803,530. That hood includes overlapped forward and rearward U-shaped body shells secured to a connector plug by means of a threaded screw at each end. An upper, rearward hood extension of the outer shell is adapted in one embodiment of the cited patent to receive a separate channel-guided clamp, secured to a lower hood extension by a fastening screw. Clamping forces between the hood extension and the clamp is established by advancing inwardly the fastening screw. This type of hood, as in the case with the previously described metal hood, also requires a number of different loose parts that must be assembled in order to form a composite hood, as well as a composite hood-plug-cable assembly.
In another hood embodiment disclosed in the last cited patent, the adjustable screw-actuated clamp is replaced by a conventional cable tie that surrounds a section of the cable jacket and hood extension. As there is no means provided in this latter hood against which the head of a cable tie can abut, the tie has a tendency to shift circumferentially as it is being drawn tightly around the cable jacket and hood extension.
In addition, as most cable ties have a relatively smooth inner major surface, or at most very minute serations, such surfaces cannot be relied upon to effectively grip the cable jacket in contact therewith. Thus, while the hood extension normally is formed with cable engaging ribs, they generally cannot be relied upon alone to provide effective strain-relief (i.e., the prevention of axial, as well as rotational displacement) for the cable during both assembly and normal use.
With respect to strain-relief per se, a commercially available molded plastic device sold by the Heyman Mfg., Co., under the tradename "Heyco", includes a molded body portion adapted to telescopically receive a portion of a pressure pad which includes a strain-relief rib, with the pad being interconnected to the body portion by a molded flexible strap or tongue. While such a strain-relief rib when formed with a semi-circular inner surface does provide substantial cable gripping action, it is not as effective and reliable as in the case where a plurality of spaced ribs would establish a circuitous cable route that would, in turn, result in a pronounced undulation in the cable. Further, the above described strain-relief device is only adapted to be resiliently force-fit within an aperture of an associated housing, there are no structural provisions to effect the desired strain-relief induced clamping force by separate means, such as with a cable tie, or an adjustable biasing member.
R. J. Guy, U.S. Pat. No. 3,936,129, assigned to the same assignee as the present invention, discloses a molded plastic hood having a composite hood extension and an integral pressure pad that cooperates with a cable tie to firmly secure a cable to the hood. The hood extension of the latter hood, however, has no provision to telescopically receive and/or otherwise key-way guide the pad therewithin so as to insure that consistently reliable clamping forces will be exerted against the outer jacket of the cable from diametrically disposed sides thereof, as is desired in order to establish the most effective type of gripping action and strain-relief. While the last mentioned hood does provide a raised boss with an eyelet therethrough that facilitates the positioning and biasing of the tie head against the boss, there is no provision that allows the head of the tie to be substantially nested in the upper portion of the hood extension so as to provide a relatively smooth, unobstructed, outer surface hood profile. Moreover, the raised boss in question must necessarily protrude upwardly from the upper surface of the main body of the hood, which unfortunately increases the overall height of the composite hood. As such, it would be particularly desirous if the integral pressure pad, rather than the raised boss in the hood extension, were formed with a recess to receive the cable tie head. This would advantageously allow the overall height of the composite hood-plug-cable assembly to be minimized.
In still another type of plastic molded hood assembly commercially available, a U-shaped clamp is adapted to simply snap-on to a receiving rearward hood extension of the hood so as to secure the cable to the connector plug. In addition to such an arrangement requiring two separate hood related parts, the snap-on clamp is not adapted to accommodate and reliably clamp cables of even closely related, but different diameters, not to mention being adapted for use with juxtaposed cables, as is sometimes desired when a given connector plug has a sufficient number of terminals to accommodate the conductors of two cables.